This paper examines the entomological investigations carried out by the French naturalist Henri-Louis Duhamel du Monceau during a series of insect epidemics that ravaged France from the 1750s to the 1780s. It shows how a particularly fierce invasion of caterpillars in the Angoumois region sparked theoretical debates about the nature of animal generation between academic naturalists, farmers, provincial officials and amateur naturalists. As part of a wider effort to reform agricultural production in France, Duhamel du Monceau sought to eliminate vernacular understandings of insect generation and to reform local pest control techniques. In his attempt to develop a body of pest-control knowledge grounded in the systematic observation of insect generation, however, Duhamel du Monceau relied heavily on the efforts of amateur naturalists.

The paper shows how he mobilized a nation-wide network of entomological observers, and collected specimens and observational reports from farmers, improving landlords and local officials throughout France. Some informants did not only act as ‘mere' observers, but formulated their own causal claims about insect generation that sometimes contradicted those of their metropolitan counterpart. The paper thus demonstrates that the “spontaneous generation controversy” was not merely an academic debate between elite natural philosophers and theologians, but that it involved a variety of actors outside academic institutions. By showing how practitioners at the margins engaged in one of the central debates of the Enlightenment, it makes the case that the “Enlightenment” was a more diffuse phenomenon than is generally recognized. It also underlines the weakness of eighteenth-century metropolitan institutions by highlighting the successful modes of resistance mounted against Duhamel du Monceau's program of agricultural reform.